The present invention relates to a tire for use on motor vehicle wheels, of the type comprising: a pair of beads each of which defines an inner circumferential edge of the tire; a pair of sidewalls, each of which is in the form of an annulus and extends in a radial direction away from one of said beads; a tread band of substantially cylindrical conformation the outer peripheral edges of the sidewalls at respective buttress areas, said tread band having a patterned annular surface at its junction with the sidewalls.
It is known that tires presently used in the automotive field have a tread band in the form of a cylindrical surface arranged to contact the roadway, two sidewalls extending in a radial direction from the opposite edges of the tread band and two beads defined at the radial inner end of the respective sidewalls along the inner circumferential edges of the tire. In known tires, the sidewalls have a substantially smooth surface on which different inscriptions such as the brand of the tire-producing company, model, particular technical data and other information, are printed.
The above inscriptions sometimes encounter some readability problems in that the contrast between the inscription surface and background surface, that is the remaining surface of the tire sidewall, is not very strong and in that the incident light on the tire sidewall, except in very favorable lighting conditions, creates two opposed circular sectors which are well-lighted but of very reduced width, whereas all the remaining portion of the sidewall is left in the shade, so that only a small part of said inscriptions is highlighted.
As regards contrast, solutions tending to enhance it have been long since adopted, such as writing the inscriptions in relief with respect to the background, knurling the inscription surface or emphasizing the edges of said inscriptions with respect to the central part thereof. These expedients have only partly solved the problem related to the inscription readability, but without dealing with the aspect connected with the tire sidewall lighting.
It must also be noted that in the tire vulcanization process carried out in a closed mold, it is required that the air that has been trapped between the mold cheek and the tire sidewall should be vented during the mold closure; in order to enable this air escape, the solutions of the known art make it necessary to form a great number of small holes on the mold cheeks which holes not only require frequent and difficult mold cleaning operations, but also give rise to the presence, on the finished workpiece, of hair-like projections consisting of the vulcanization stems created by the elastomeric material which penetrates into the small holes during the vulcanization step. These unaesthetic hair-like projections must be eliminated by carrying out a finishing operation on the vulcanized tire.
In addition to the above, a correct and optimal distribution of these small holes on the mold cheek for air escape purposes would inevitably involve the presence of some small holes on the inscriptions as well or in close proximity thereto: but since the relative hair-like projections would aesthetically impair these inscriptions to a great degree, it is better to form a greater number of small holes, provided that they are far from the inscriptions.
From the U.S. Pat. No. Design 87,418 a tire for motor vehicles is known which has the sidewalls devoid of informative inscriptions and a rounded-profile tread. Two series of grooves depart from the tread center line of said tire and they symmetrically extend on the opposite sidewalls of the tire up to the bead area.
In this tire the problem related to the sidewall hair-like projections seems to be overcome by renouncing the inscriptions and through a plurality of grooves extending radially from the bead to the buttress and circumferentially distributed on the tire sidewall, which grooves constitute the prolongation of the tread pattern grooves. Since these grooves ensure air escape towards the tread, they make it useless to provide small venting holes on the mold cheeks.
In accordance with the present invention, the Applicant has found that by defining at the tire sidewalls an annular strip having a plurality of circumferentially distributed ribs crossing the annular strip itself, it is possible to affix informative inscriptions on the surface of said strip, the readability of which is greatly improved while at the same time achieving a better luminosity of the whole tire sidewall and important advantages from the production point of view.